The present invention relates to a method and apparatus for working an X-ray mask in which in an X-ray mask or the like is used in X-ray lithography or the like. A focusing ion beam which works a product covered with a protective film is positioned with a high degree of accuracy to a defect or the like, thereby eliminating the defect of the product.
In recent years, in association with the realization of a high integration in a semiconductor integrated circuit, an X-ray exposing method is used to form a fine pattern. According to this method, an Si wafer or the like coated with a resistive material adapted to be photo-sensitive to the X-ray is exposed by use of an X-ray mask which is constructed by forming a circuit pattern of heavy metal on a thin supporting material (membrane). Since the wavelength of an X-ray is extremely shorter than that of the light, a accurate circuit pattern can be formed and the X-ray is also superior to an electron beam exposure method or the like with respect to the mass productivity. FIGS. 1 and 2 show arrangements of a mask 200 for X-ray exposure (hereinafter, referred to as an "X-ray mask"). In FIG. 1, a thin film membrane (supporting material) 202 made of BN (boron nitride) or the like is formed on an Si wafer (holder) 201 from which a portion 201a was removed. A plating electrode 203 is formed on the membrane 202 and an insulative film for plating stencil (negative form) is formed. Thereafter, this insulative film is eliminated by a dry etching. After that, a circuit pattern 205 is formed by plating. A protective film 204 is coated on the electrode 203 and circuit pattern 205. In this manner, the mask 200 is formed. The central portion of the Si wafer 201 is eliminated by etching, thereby forming the hole 201a so as to enable the X-ray to be transmitted.
FIG. 2 shows another example. A thin film (supporting material) 302 made of silicon nitride or the like is coated onto an Si substrate (holder) 301 having a hole in the central portion. A heavy metal layer is formed on the thin film 302. Thereafter, a circuit pattern 305 is formed by dry etching. A protective film 304 is coated on the thin film 302 and circuit pattern 305.
The reason why the final product of the X-ray mask is formed by coating the protective film 204 or 304 is because in the X-ray exposure, the secondary electrons or Auger electrons which are generated when the X-ray is irradiated onto the circuit pattern 205 or 305 are absorbed by the protective film 204 or 304 so as not to be irradiated onto the wafer, thereby enabling a fine circuit pattern to be exposed and formed at a high accuracy. In addition, the protective films 204 and 304 also obviously protect the circuit patterns 205 and 305 from external stress. On the other hand, if the defects were corrected and eliminated before the protective film 204 or 304 is coated and formed, defects are caused due to the mixture of foreign matters when the protective film 204 or 304 is formed. FIG. 3 shows an example of a defect. In the diagram, (a) shows a black dot defect (opaque defect) caused when an additional pattern was deposited to a normal circuit pattern. (c) shows a blank defect (pin hole defect) caused when a normal circuit pattern was notched. If such a defective circuit pattern is directly copy transferred, this will soon result in a defect of the circuit pattern of an LSI. To prevent this drawback, the defect needs to be corrected at the stage of the copy transferring process (exposure process) of the X-ray mask as shown in (b) and (d) in FIG. 3.
However, the circuit patterns 205 and 305 of the X-ray masks are so fine that have the widths of 0.5 .mu.m or less. Moreover, their heights are set to large values of 0.5 .mu.m or higher in order to absorb the X ray. Hitherto, the black dot defect has been corrected by performing a laser work to the photo mask. However, it is difficult to correct defects of such a fine pattern due to the fact that such work is done by a laser and is thermal work, and there is a focusing limitation of the laser beam due to the diffraction, and the like. Therefore, in a recent correcting method, such defects are corrected by irradiating a focused ion beam on the order of submicrons as disclosed in JP-A-58-56332.
The foregoing conventional technique is insufficient in terms of the detection of the pattern and defects covered by the protective film as in the X-ray mask and LSI. That is, in the X-ray mask, LSI, or the like, a protective film made of polyimide or the like is generally formed onto an absorber pattern so as to flatten it is shown in FIGS. 1 and 2. An ion beam is scanned and irradiated onto this sample and the secondary electrons or secondary ions which are generated from the sample are detected. Only the roughness (concave and convex portions) of the surface is detected by a scanning ion image which is displayed on the display by modifying the intensity of the spot scanned synchronously with a scan signal in proportion to the intensity of the secondary electrons or ions obtained. This is because the projection range of an ion beam used is so short, about 1000 .ANG. or less and only the information of the surface is derived. Thus, there is a problem such that it is hard to detect the fine pattern and defects from over such a protective film and it is fairly difficult to correct them.
In addition, as conventional techniques, there have been known U.S. Pat. No. 4,683,378, EPC Application No. 85108708.0 (laid-open No. 0168056), and U.S. Pat. No. 4,503,329, EPC Application No. 82109014.9 (laid-open No. 0075949).